1. Field of the Invention
The present invention relates to fiber optic hydrophones. More particularly, this invention pertains to a hydrophone formed in multiple segments.
2. Description of the Prior Art
SONAR-based systems for detecting underwater hazards and threats employ pressure-actuated transducers of the hydrophone type to generate signals indicative of the presence and location of underwater objects. In an active system, such objects are "illuminated" by the reflection of acoustic wavefronts that are initially transmitted from a ship or other source in the water. The acoustic signals, when reflected, provide phase shift information that, when processed, enables one to ascertain underwater position. In a passive system, noise that is radiated from a target is detected.
In use, a SONAR system utilizes a predetermined submergeable arrangement of acoustic hydrophones to collect a spatial distribution of "echo" data that can be analyzed for information such as position and closing rate.
The array is housed within a hose-like element that is fixed to the end of a towing cable that comprises an arrangement of optical fibers and/or electrical conductors located within a protective outer jacket. An example of such a cable is disclosed in U.S. patent Ser. No. 4,952,012 of Stamnitz entitled "Electro-Opto-Mechanical Cable For Fiber Optic Transmission Systems."
The processing of data from a array is well-known and discussed, for example, by A. Dandridge et al. in the article "Multiplexing of Interferometric Sensors Using Phase Carrier Techniques," Journal of Lightwave Technology, Vol. LT-5, No. 7 (July 1987) at pages 947-952.
While the towed array is a well accepted and recognized element of a SONAR system, its realization and practice is fraught with a number of serious mechanical difficulties. Some of such problems are related to deployment of the array while others pertain to the maintenance of reliable optical and/or electrical contact between it and the SONAR-equipped ship. The prior art discloses fiber optic hydrophones of various sizes and shapes. For example, hydrophones for towed arrays have been manufactured by the Assignee herein having a diameter of one inch and a length of six inches and having a diameter of 0.5 inches and a length of three inches. Both of such units comprise rigid body constructions and are representative of the majority of fiber optic sensor designs of which the inventors are aware.
In use, a hydrophone array is generally stored and played out from a winch aboard a transporting ship. In deployment, the array and cable may also traverse various capstans, pulleys and other sheave-like devices for guiding the cable over the ship's deck. While hydrophones having lengths as above-described are quite suitable when used in an environment where winches and sheaves possess radii of greater than twenty (20) inches, the rigid sensing elements are not suitable for use in an environment where very small radius (.congruent.2 inches) sheaves and winches are encountered. When an array of three (3) or six (6) inch sensors is spooled over a two inch radius winch, it is obvious that stresses will be produced in both the hydrophones and the array's encapsulating hose that can degrade performance and possibly cause the failure of both. For example, the rigid hydrophone may become bent during storage or the array's hose-like housing may be punctured.